1. Field of the Invention
The present invention relates to an antenna arrangement for a radar surveillance technique for target locating having altitude acquisition in which, for the purpose of level comparison, a plurality of mutually overlapping radiation lobes lying above one another are generated by a reflector rotating together with an essentially vertically arranged primary radiator row around a vertical axis.
2. Description of the Prior Art
Standard radar surveillance antennas only supply the azimuthal position of the target but not, however, its angle of elevation. Given increasing flight density and for a more accurate vectoring of target tracking system, however, the additional information concerning the altitude of the target and the angle of elevation of the target is of ever-increasing significance.
Surveillance antennas are usually constructed as reflector antennas having a double-curvature reflector. The expansion of such an antenna for altitude determination by means of additional primary radiators is not practically possible because of the vertical reflector curvature which, given the necessary deflection, produces phase errors which are too great.
It is known to employ two separate radar systems for target locating according to azimuth and elevation angles, whereby one surveillance radar serves for determining the azimuthal angle and an altitude search radar having a vertically slewable beam serves for providing the elevation angle, the altitude search radar being vectored by the surveilance radar. Thereby, however, temporal delays and difficulties arise in the construction of the double antenna arrangement, particularly in the design of the swivel base of the altitude acquisition antenna.
In so-called 3-D radar, only a single, common antenna arrangement is provided for acquiring the azimuth and the elevation of a target, whereby only a mechanical beam slewing is considered for the horizontal acquisition and electronically phase-controlled beam slewing is preferred to the mechanical beam slewing for the vertical plane because of the swiveling of a large antenna thereby required with the mass accelerations resulting therefrom. In addition to the high expense of the phase control, the disadvantage of such an arrangement is that the scanning must occur relatively quickly because of the additional horizontal search movement and, therefore, the dwell time necessary on the target for a secure identification of the target position is not achieved.
However, surveillance radar antennas are possible in which both the horizontal and vertical beam motions occurs by a phase-controlled single radiator group. This, however, represents an extremely high expense which is not appropriate for many constructions.
A better possibility for the simultaneous acquisition of azimuth, range and elevation of a target occurs by employing a plurality of receiving lobes lying above one another and overlapping in the vertical pattern, whereby the angles of elevation of the lobe intersections are known and the angular distance of one of these points of intersection can be identified by level comparison of the two appertaining lobe echoes. In this method, it is known in the receiving and transmitting cases, to employ the same antenna with a single parabolic reflector and a plurality of primary radiators which entirely, or partially, illuminate the parabolic reflector from different angular positions, so that variously inclined lobes, and lobes of differing width, are generated. Usually, a section of a paraboloid of revolution is thereby employed as the reflector and a vertical primary radiator row (stacked beam) is arranged around the focal point of the reflector, so that the desired radiation lobes lying above one another and overlapping somewhat arise. Given more greatly deflected beams whose excitors are at a greater distance from the focal point of the reflector, however, the gain decreases and the side lobes increase, thereby limiting the available angle of elevation range. Since the individual lobes are usually employed in the receiving mode, the transmitting antenna, if it is not to be realized by an additional reflector antenna, must be realized by the interconnection of the individual primary radiators in the transmit case given separate receiving evaluation. Such an interconnection of primary radiators, however, leads to an extravagent switching matrix and to lobings of the transmit antenna pattern.
Such surveillance radar antennas are described in the German Letters Patent No. 2,016,391.